Hygroscopicity risk and organic-inorganic hybrid perovskites easy decomposition in solar cells limit their usefulness. Apart from the hybrid organicinorganic perovskites, inorganic perovskite solar cells display a better stability toward moisture, light soaking, and thermal stressing. However, most inorganic perovskites are inappropriate for single junction or tandem solar cells due to their large bandgaps (>1.8 eV), which eventually results in light absorption loss. Fortunately, cubic CsPbI 3 perovskite (having 1.73 eV bandgap) could potentially serve as top cells in tandem devices with silicon solar cells. Poor phase stability of CsPbI 3 is considered a major obstacle to design CsPbI 3 perovskite solar cells. This review highlights the most recent studies on the progress in CsPbI 3 -based solar cell device field. Moreover, this review also summarizes certain strategies to improve phase stability, such as size reduction to nanocrystal or external cations/anions doping, with the aim to improve the devices design.

HIGHLIGHTS• Lead-based halide perovskite materials have revealed excellent properties in optoelectronic applications. However, the material stability and the toxicity of lead still hinder their large-scale commercial applications.• Lead-free halide double perovskite materials possess the characteristics of environmental friendliness, exceptional stability and tunable optoelectronic properties.• A limited number of halide double perovskites have been synthesized, and extremely few have been developed for optoelectronic applications. Continuing effort is needed to explore more halide double perovskites and modulate the properties for their further applications.ABSTRACT Lead-based halide perovskites have emerged as excellent semiconductors for a broad range of optoelectronic applications, such as photovoltaics, lighting, lasing and photon detection. However, toxicity of lead and poor stability still represent significant challenges. Fortunately, halide double perovskite materials with formula of A 2 M(I)M(III)X 6 or A 2 M(IV)X 6 could be potentially regarded as the films still manifest low quality for photovoltaic applications. Therefore, we propose that continuing efforts are needed to develop more halide double perovskites, modulate the properties and grow high-quality films, with the aim of opening the wild practical applications.

Low‐cost solution‐processed lead chalcogenide colloidal quantum dots (CQDs) have garnered great attention in photovoltaic (PV) applications. In particular, lead selenide (PbSe) CQDs are regarded as attractive active absorbers in solar cells due to their high multiple‐exciton generation and large exciton Bohr radius. However, their low air stability and occurrence of traps/defects during film formation restrict their further development. Air‐stable PbSe CQDs are first synthesized through a cation exchange technique, followed by a solution‐phase ligand exchange approach, and finally absorber films are prepared using a one‐step spin‐coating method. The best PV device fabricated using PbSe CQD inks exhibits a reproducible power conversion efficiency of 10.68%, 16% higher than the previous efficiency record (9.2%). Moreover, the device displays remarkably 40‐day storage and 8 h illuminating stability. This novel strategy could provide an alternative route toward the use of PbSe CQDs in low‐cost and high‐performance infrared optoelectronic devices, such as infrared photodetectors and multijunction solar cells.